1. Always have an up-to-date antivirus software installed on your personal computer(s).
2. Update ALL of the software you use regularly. This is important because vulnerabilities in software are always being discovered and they don't discriminate by platform or vendor.
3. Use a firewall. No connection is safe without one.
4. Be smart with your email. Don't open suspicious or sketchy emails and their attachments. Open and read your emails in plain text format, this offers important security benefits...unless you really must see the pretty looking colors and fonts.
5. Avoid all anonymous file-sharing sites like the plague. These sites are packed with worms, trojans, viruses, adware, and spware. (ex. Torrent, Kazaa)
One of my favorite things to do on my PC is to download and watch movies. I bet many of you reading this do the same. Just know that many of those streaming websites where users can upload copies of movies are most likely riddled with different forms of viruses and spyware, and are therefore one of the more dangerous things you can do on the internet.
With all of that said, it is important to remember that there is more good than bad out there on the internet. The goal is not to be paranoid, it is to be informed, aware, and cautious.
After reading this list of tips, how well have you been protecting yourself recently?
Sources:
http://antivirus.about.com/od/securitytips/a/safetytip.htm